Control system



.Nov. 8, 1949 H. C'ONVISER 2,487,697

CONTROL SYSTEM Filed Feb. 18, 1946 3 Sheets-Sheet l 1 1 13 ML 6kINVENTOR m- HHHHY [UAW/55H l 0 BY k 5 TORNEY H. coNvlsEr -CONTROL SYSTEMNov. 8, 1949 5 Sheets-Sheet 2 Filed Feb. 18, 1946 INVENTOR HHRHYL'UNV/EEH ZTORNEY H. CONVISER Nov. 8, 1949 CONTROL SYSTEM Filed Feb. 18,1946 5 Sheets-Sheet 3 INV ENTOR HHHH Y L'UN V/SEH @ZRNEY 2205.rZmEuUjmQQ Patented Nov. 8, 1949 CONTROL SYSTEM Harry Conviser,Ardsley, N. Y., assignor to'Bendix Aviation Corporation, Teterboro, N.J.-,- a corporation of Delaware Application February 18, 1946, SerialNo. 648L490 2 Claims.

This invention relates generallyto control systems-such asa'utomaticsteering systems for air or" water craft, for example, and moreparticuany t'o'novel" coupling means for such systems with the use ofwhich a definite time lag may be interposedbetween the" response of onecircuit of thes'ystemto the operation of a second circuit.

Control systems of this general character are represented by copendingapplication Serial No. 562382 3 filed" November 1-0', 1944, now Patent2,432,036, and-are adapted for use with automatic steering systems for'aircraft, such systems embodying a thermal delay coupling device,operating. on a heat exchange relation for providing, whenuse'd inconnection with direction, direction rate, bank or pitch displacementsignals, automatic trim functions or, when used in conne'ctionwithrudder, aileronor elevator follow-up signals as an anti-huntingexpedient. When a craft, provided with such a system, was subjected toa" persisting displacement signal, the thermal delay coupling wasoperative to provide an average displacement signal suppliedto theparticular control surface being considered for returningtoandmaintaining the craft in a reference position whether in azimuth orin attitude.

The system described" in the copending application relied primarily upona heat exchange principle so that a relatively long period was injected'between the response of one circuit to the operationof a second'circuit.In some instances, it is desirable to provide a time delay couplinghavinga' more rapid. time constant than that of the" c'o'pendingapplication and to this end the novel system of the present invention isprov scribed course and/or in a predetermined attitilde".

Another object of the invention is to provide a novel automatic steeringsystem for mobile craft, adapted for' uppressing hunting thereof about2. operation of the craft is obtainedand/or' adapted for returning andmaintaining a craft substan-' tially in datum after a change indisplacement due to a change in load moment;

A further object is to provide a novel anti hunting provision inthenature of an error averaging mechanism having a rapid time constantfor an automatic steering. system for mobile craft whereby the craftwill be provided with proper dampening about any one or all of itscontrol axes.

Another and further object is to provide a novel and relatively simpleautomatic trim arrangement for automatic control systems for mobilecraft.

A further object is to provide a novel time delay device'having a rapidtime'c'o'nstant and operating on a temperature rise rather than a heattransfer or exchange principle.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawings. It is to beexpressly understood, however, that the drawings are for purposes ofillustration only and are not intended as a definition of the limits ofthe invention.

In the drawings wherein like reference characters refer to like partsthroughout the several views,

Figure 1 is a wiring diagram of a conventional Wheatstone bridgecircuit;

Figure 2 is a wiring diagram ofthe main bridge circuit of Figure 1 withthe resistor of one arm thereof replaced by a second control bridge circuit;

Figure 3 is a view similar to Figure'2 with two adjoining arms of themain bridge comprising two control bridge circuits;

Figure 4 is a diagrammatic illustration of an automatic steering systemfor one control axis of a mobile craft incorporating the" novel subjectmatter of the present invention in the followup channel thereof; and,

Figure 5 is a view similar to that of Figure-'4 having the novelprovision of the present invention applied to the displacement channelthereof.

Referring now to the drawings for a more detailed description and moreparticularly'to Figure 4 thereof, the novel delay coupling of' thepresent invention issho'wii applied to an automatic pilot of the generalcharacter shown and described in copending application Serial No.516,488 filed December 31-, 1943. I he displacement signal forcontrolling the position of a control surface in is derived from asignal generating device, generally designated with the referencecharacter I l, which device may comprise the gyro stabilized magneticpick-up device of the latter application where the present invention isapplied to automatic rudder trim or which may comprise the electricalpitch or bank take-oil of the aforementioned application where theinvention is applied to automatic elevator or aileron trim.

As more fully described in copending application Serial No. 516,488, thedisplacement signal is fed by generator I! through conductors l2 and I3to the grid M of a tube 35 of a servo amplifier l5. 7

Plate of tube i5 connects through parallel conductors i8 and 59 withgrids Ell-and 2| of tubes being connected by way of conductors 26' and2'! with a split secondary winding 28 of a transformer whose primarywinding 29 connects with a suitable source of alternating current (notshown) such as the crafts power supply.

Magnetic reactors 36 and 3| are provided between each plate 24 and 25and its related connection with secondary winding '28. Each of thereactors comprises a soft iron core (not shown) having primary windings32 and 33 connected in series with each other and with the currentsource through leads 34 and 35 which may be tapped to the leads feedingprimary winding 25. Furthermore, each reactor is provided with asecondary winding 36 and 3? which are connected in series opposedrelation and have output leads 38 and 39. In addition to the primary andsecondary windings, each reactor is provided with a saturating winding43 andlll connected with leads 26 and 21.

Output leads 38 and 33 of the series opposed secondaries connect withone phase winding 42 of a two phase motor 43, whose second or fixedphase winding 44 is connected with the crafts source of power. Motor 43is adapted for driving a servo motor 45, connected through cables 46with control surface i0, through a gear reduction system 4'! and anormally engaged solenoid operated clutch 48.

With the craft in a predetermined attitude, with no apparent deviationabout its pitch axis, for example, the signals at grids 2t and 2! fromgenerator I! are at zero so that the network is balanced and the currentat output leads 38 and 39 of the reactors is zero because secondaries 36and 3'! are in series opposed relation so that induced currents in onesecondary balance the induced currents in the other secondary.

Upon the occurrence of a deviation from a predetermined attitude asignal will be developed by generator I I which may be considered to bepassing from zero to a positive maximum value at grids 25 and 2| oftubes 22 and 23. Assuming that, at that moment, the current at plate 24of tube 22 is passing from zero to a positive maximum value, the currentat plate 25 of tube 23 will be passing from zero to a negative maximumvalue so that no current will flow in saturating winding 4|. Current,however, of a pulsating character will flow at lead 26 and, therefore,within saturating winding 40 as a result of which the core of reactor 30will become saturated so that currents induced in secondary 35 will bedecreased causing network unbalance and creating current flow in onedirection within leads 38 and 39 to energize motor 43.

If craft deviation is in a direction opposite to that above described,the signal from generator I! impressed on grids 20 and 2| will be ofsuch a and also to impart stability to the craft to prevent oscillationthereof, an electrical follow-up system is provided in the nature of aninductive device 49 comprising a wound stator 55 energized from thecraft source of supply and an inductively coupled wound rotor 5| whichis mounted by a shaft 52 for angular motion by motor 43, the drivingconnection between the motor and the rotor being a permanent one andindependent of whether or not clutch 48 is engaged or disengaged.Normally, rotor 5| is maintained in a null position, i. e., one in whichthe electrical axis of the rotor winding is normal to the resultantmagnetic field at the stator. Motion from the null position on the partof rotor 5|, during operation of motor 43, causes the inducement of asignal within the rotor winding which is led off and impressed upon gridI4 of tube l5 by way of conductors 53 and a transformer 54, having aprimary 55 and a split secondary 56 and 5'! the purpose of which willhereinafter appear. The signal generated within rotor 5| is inopposition to the displacement signal within generator H and increaseswith increased motion of surface It until a given point is reached, atwhich time the signal of rotor 5| is exactly equal and opposite to thedisplacement signal to thereby Wash out the displacement signal at whichtime motor 43 is de-energized and control surface H] has attained adeflected position proportional to the displacement signal.

With the surface [0 in its applied position and motor 43 de-energized,the craft begins to return to its prescribed reference. In doing so, thedisplacement signal developed by generator I I starts to diminish invalue while the follow-up signal of rotor winding 5|, being at amaximum, becomes predominating and energizes motor 43 in a reversedirection to start bringing surface Ill back to a neutral position,motor reversal being determined by current flow in an opposite one ofsaturating windings 40 or 4| to the one having current flow therein uponinitial craft departure from datum as explained above. With reversemotor operation, the signal in rotor 5| diminishes until the rotorattains its null wherein, unless another displacement signal originatesat generator I, the control surface and generator will be insynchronism. For further stability and prevention of over control, arate of displacement signal may be utilized in addition to thedisplacement signal for controlling surface It] in the manner fullydescribed in copending application Serial No. 516,488.

As pointed out in copending application Serial No. 562,823, now Patent2,432,036, under control will occur in the steering system described inthe event of a load change so that the craft will not be returned todatum but to some attitude parallel to datum. This means that theoriginal trim adjustment which maintained the craft in datum is nolonger satisfactory for the new condition due to load change. By meansof the present invention a novel arrangement is provided which providesthe necessary additional signal for autogroomer" maticaily supplementingtiic' original min-adjust ment' to return the crart-substantlany toasthma In place of the heat exchangEontralns-frde vice of copendingapplication Serial Na 562823,

present invention a" novel time new cou ling utilizing" atemperature-change principle-thereby having amore-rapid time constantthan device's heretofore known orthis character: For a 'bett'erunderstandiii'ggoi thepresent inventiom reference is made to=-Figure-1or the drawings where four resistors 60": 6'1 6? and Baaresh'ovmarranged-in a conventional Wheatstone bridge cir'cuiti- Theresistors-are of equal value so-that ifa voltage isapliedto the bridgeacross condiictors fl and W no-voltage wili appear-*at oonductcrs- 6'6and' '61 since the'se points are of equal potential, con"- versely; if avoltage is 'a'ppli'ed at'oonductors" 86,- 61 no v01tage"-- will appearat conductors 64 65. It"hasbeen-discoveredthat wo voltagesiofsimilar orwidely: varying magnitude, frequency an'dlor wave-formmay b'e"=simultaneously applied across conductors 6'4;- I55 and- 66 6 F;respectivelyawithout any interaction-- or frequenoy oiphase''dist'ortion. I n= conformance with thischaracteristic; one arm of thebridge ofFigure constituted by resistor 63, for example, may hereplaced; assho'wn in Figure 2, by fbur' equal heat responsiveresistors- 68- 69, 141 and 1 l arranged in a bridge which may constitutean auxiliary or controi bridge for:

the main bridge.- opposite corners'ofthe control bridge are connected:byway orconductors 12: to a source of signal voltage:and 'with:theappearance of at-signal across conductors: 1 2 current will flow through thefour arms or control-bridge but nointeraction will result betweeri -thatcurrent and the current of the: main brldg'e, Currentflow in the controlbridge, however; manifests itself in atemperature -ri'se in the: arm-ofthe main bridge constitiited hy the: control:- bridge to therebyunbalance the main bridge whereupon current from conductors 645 and-1iwillfiow' at conductors 66 and S-IQ- By furthen replacing resistor 62 oftheibridge of Figure 1" with four: equalheat responsive re sistors 13,1'4; l5land lfi arranged -in the form of a secondauxiliary or controlbridge: as s'hown in Figure 3 and connecting opposite corners-of thelatter control bridge-byway of conductors 1-! to a source of'signailvoltaga-thedirection of-cur rent flow a-t'output conductors 66,- 61 05the main bridge m'a-y loo-reversed depending upon whether signalvoltagesare applied to -conductbrs fl or i! or the cont-rol brldgesa In thismanner, by applying a direct current, or rectified cur-rent; pulse,squarewave or distorted wave or any frequency to conductors I? or TF'ofthe control bridges, a-s-i'ne' wave or any other desired wave form maybecontrciled at the main bridge in mag'nitude and/orpolarity;Tliegeneral arrangement ofFigure 3*t-hus constitutes' a time delaydevice constitutingthcsubject matter-of the pres ent' invention havingarapid timemonstantand 'aidapted for usewher'e'v'er a definite time lagis'desired between acontrolled circuitin its response totheorierationofa con=trolling-' circuit. If desired; moreover, the' two controlbrid'g'es' maybe arran-ged an'd' constructed'=-in-t-he"form of a sealedor'vacuum tube as-shown iircopending application' Se'riaPNo; 6485493filed =February,r8;- I946.

, For-purposes of providing an" automatic trim provision forthe-steering. system-liereina'bove described; the novel time" delay"device hereof is shown Figured as applied to the follow-up channelofthe" system. Tothisendj conductors 1-2' of one 1 control bridge: areconnected across; a secondary T8- of a transformer 19: whose. primaryBit-is in circuit with aplate- 8l of: aid'ual tribdc tube 82 whileconductors-1 1: of the-second control bridge are connected acrossasecondary 8& ot a transformer whose-primary 'SSisdn cirGuit with aplate 86 of tube 82. Grid-8 1 of the tube i's com nected with one end ofsecondary Winding- 51 0f transformer 54 while gr-id 88 -'is'connected-withthe' opposite end of the secondary, the latter being center tappedand grounded asshown; Output conductor 61 of the main bridge isconnectedtd grid H!" of" tube l 5 while outputconductor 8R isconnectedto one en'd of secondary winding 56',- the' other'end of which,likewise, connectswith g'ri'd' l4.

For a single and minor displacement" of the craft from courseorattitudeer-signal is I developed by generator ll and'amp'l-ifi'ed toenergizemotor 43* whereby control surface Ill is actuated to change craftcourse" or attitude; Operation of motor 43 displaces rotorwinding 510fthe inductive follow-up device to develop a fo1low-'up"sig-'naltherein which is communicated through leads 53 and transformer 54-through' secondary 58 thereof to be impressed upon the displacementsignal at grid I i". Even' though some signal" is communicated to grids81' and 8 8of tube82 it isinsufllcient to make the time delay couplingeifective.

If; on the other h'and', the displacement is of a persisting character;current flow" develops at plate 81 or'BG; depending'uponthe direction ofthe follow-up signal, to provide a signal at'e'ither secondary 1801 83'to-provi'd'e current flow atcon trol bridge con'd'u'ctorslZor 1T;'I'hetemp'eratur'e of the controibridge receiving the currentri'ses tothereby. unbalance the main bridge whereupon currentfrom thesourcefeeding'conductors'fi'fand B5 flowsat output conductors G'Band'(iTt'o lie-impressed upon the displacement and'follow-u'p signal atgrid. M on tube I51 The action of the time delay coupling is-of suchacharacter as to develop a further or average displacementsignalWhereuponv the craft is-ret'urned to its-datumin. the face of theexistence of the persisting displacement signal.

While the arrangement has. been illustrated and. described hereinabove':in connection with the follow-upsigual channel to provide-automatic trimcontrol,. it may be applied; equally as well directly to thedisplacement signal 'channel where it will act'in the nature'of adifierentiationmech= anism. to impress upon the d'isplacem ent signal?-a corrective signal: which will apply? a dampening factor to preventcrafthunting, such application being adapted for use-in with: any one orall'of the three axes of'craftcontrolf Tothis end the arrangementofFigure 5 is provided which com-'- prises substantially the automaticcontrol 'of Figure' i in that normally adisplacement'signa'l originatingin generator H is impressed upon grid [4 of tube 15 and ultimatelyenergizes servomot'or 43 to operate control surface Ill; In response toservomotor operation, a follow-up signal is' de= veloped at rotorwinding 51' to beimpressedupo'n the displacement signal substantiallyin" the man"- ner' described in connection with Figure-4.

The displacement signal from generator H is fed to grid l4'of' tube l5by way of conductors l2 and i3 which are connected across the primarywinding -01 a transformer 91 having two secondary windings 92 and 93,.winding: 52 communicating by leads Si l with thegrid' M of tube f5;Seoondary winding 93, on the other hand, is center tapped and groundedas shown, and connects by means of leads 95 with grids 96 and 91 of adual triode tube 98. Plate 99 of the tube'connects with one end of acenter tapped primary winding I of a transformer IOI having twosecondary windings H12 and I03 while plate I64 connects with theopposite end of the primary winding. Tube supply is provided byconductors I65 con nected with the tube cathodes and a center tap ofprimary Winding I66. The main bridge supply is fed by conductors 64 and65 while the output leads of the main bridge are constituted byconductors I66 and I51, the former being connected with one ofconductors 96 for impressing a signal on grid Id of tube i5 and thelatter being connected with rotor windings 5!, one end of the latterbeing grounded as shown.

Assuming displacement in azimuth, generator I l develops a signalproportional to such displacement to energize servomotor 43 and operatethe control surface. A follow-up signal is developed at rotor wnding 5|as a result of servo operation and such signal is fed by way ofconductor I 61 through the main bridge of the time delay coupling andconductor I66 to be impressed upon the displacement signal on grid I4 oftube I5, such displacement signal through secondary winding 92 to thetube. Assuming, further, a persistent displacement defined by a seriesof course departures due to given disturbances, the displacement signalwill, in addition to being impressed upon grid I l, be also impressedthrough secondary winding 93 on either grid 9-5 or 91 so that currentwill flow at either secondary winding I62 or I03 and, therefore, withinits related control bridge. Even though current flow within one of thecontrol bridges does not interact with the current of the main bridge itresults in a temperature rise of the arm of the main bridge defined bythe particular control bridge having current flow therein to therebyunbalance the main bridge whereby current flow therefrom throughconductor I06 to grid I4 of tube I5. The signal of the time delay devicerepresents an average error signal and is impressed upon thedisplacement and follow-up signal at grid Id of tube I5 to bring andthereafter maintain the craft on a substantially predetermined course orattitude.

Except for the fact that the present invention provides a novel timedelay coupling having a rapid time constant and utilizes a temperaturerise characteristic to unbalance a normally balanced electrical networkand thus provide a definite time interval between the response of onecircuit to the operation of a second circuit, the theory and operationthereof in connection with its application as an automatic trim orantihunting provision for aircraft is generally similar to theory andoperation of the heat exchange or transfer coupling and its applicationthereto more fully described in copending application Serial No.562,823, now Patent 2,432,036, reference being made thereto for thispurpose.

There has thus been provided by the present invention, a novel timedelay coupling having a rapid time constant for injecting a definitetime interval between the response of one circuit to the operation of asecond and controlling circuit. When applied to an automatic steering orcontrol system for mobile craft, the novel coupling device hereofprovides a relatively simple automatic trim provision and/ or dampeningmeans for preventing craft hunting about any or all of its axes ofcontrol. The specific automatic steering system utilizing the novel timedelay device hereof is claimed in divisional application Serial N 0.88,657, filed April 20, 1949. a Comparison tests for wires ofapproximately equal diameter on sensitivity and time constant have shownthat for equal wattage applied, the arrangement. of Figure 3 hereof wassubstantially thirty times as fast andgave five times the output voltagefor one-half the bridge voltage applied to a heat exchangeor transferdevice of copending application Serial No. 562,823, new Patent2,432,036. Moreover, the time constant of the coupling of Figure 3 canbe controlled by the heat capacity ofthe wire, the supporting mounts andthe atmosphere within which it is enclosed.

Although but a single embodiment of the invention has been illustratedand decribed and its application shown to two specific uses, i. 6.,automatic trim and anti-hunting for craft automatic steeringsystems,various changes and modifications in'the form and relative arrangementof the parts, which will now appear to those skilled in the art, may bemade without departing from the scope of the invention. Reference istherefore to be had to the appended claims for a definition of thelimits of the invention.

What is claimed is: x

1. In combination with a controlled circuit and a controlling circuit, atime delay, coupling connecting said circuits comprising a firstnormally balanced electrical bridge circuit having connections acrossone of its diagonals to a source of current and across the-other of itsdiagonals to said controlled circuit, a control bridge circuitcomprising one arm of'said first bridge circuit having connectionsacross one of its diagonals to, said controlling circuit and across theother of .its diagonals to said first bridge whereby in response tooperation of said controlling circuit the temperature of said controlbridge is changed to thereby unbalance said first bridge whereby uponthe occurrence of a predetermined interval of time following theoperation of said controlling circuit current flows to said controlledcircuit in one direction from said source, and a second control bridgecircuit comprising a second and adjoining arm of said first bridgecircuit having connections across one of its diagonals to saidcontrolling circuit and across the other of its diagonals to said firstbridge whereby in response to operation of said controlling circuit thetemperature of said second control bridge is changed to therebyunbalance said first bridge whereby upon the occurrence of apredetermined interval of time following the operation of saidcontrolling circuit current flows from said source to said controlledcircuit in an opposite direction.

2. A control circuit comprising a normally balanced main electricalbridge having one diagonal thereof connected to a source of current,output conductors associated with the remaining diagonal of said bridge,a control bridge comprising one arm of said main bridge and havingconnections across one of its diagonals to a second source of currentand across the other of its diagonals to said main bridge, and a secondcontrol bridge comprising a second and adjoining arm of said main bridgeand having connections across one of its diagonals to said second sourceof current and across the other of its diagonals to saidm ain bridge,one or the other of said control bridges being adapted for energizationby said second source of current whereby the temperature of theenergized control bridge changes to unbalance said main bridge to causecurrent from said first source to flow in one direction or another atthe output conductors of said main bridge upon the occurrence of apredetermined interval of time following energization of said energizedcontrol bridge.

HARRY CONVISER.

REFERENCES CITED Number UNITED STATES PATENTS Name Date Stone Aug. 16,1904 Boykow Oct. 17, 1933 Fitz Gerald Feb. 16, 1934 Moseley Aug. 16',1938 Whittle Dec. 1, 1942

